1. Field of the Invention
The present invention relates to an information processing system and a method of allocating an I/O to paths in the information processing system. More particularly, the present invention relates to a technique which is used in an information processing system having an information processing apparatus and a storage apparatus coupled to each other through a plurality of paths, and which appropriately allocates an I/O to each path.
2. Related Art
As an objective of improving performance of a storage system having a configuration in which an information apparatus and a storage apparatus are coupled to each other, various research and development efforts have been made on how to issue I/Os (data input/outputs) exchanged between the information apparatus and the storage apparatus.
For example, Japanese Patent Application Laid-open Publication No. 2002-197046 discloses an algorithm for determining the schedule of I/O disk access based not on the priority of I/Os, but on the processing deadlines of the I/Os in order to allow a request with low priority in a queue to be preferentially provided even when there is a request with high priority.
In the meantime, where data input/outputs requests to a storage apparatus are distributed to each input/output paths by using a round-robin method, there is a problem that the data input/output requests of higher priority cannot be preferentially transmitted to the storage apparatus when there is a flood of data input/output requests to the storage apparatus. In order to solve this problem, Japanese Patent Application Laid-open Publication No. 2004-185327 discloses that a usage rate of each logical path is compared with a determination value and that, based on the comparison result, the data input/output request is switched to a control to be transmitted to the storage apparatus through a logical path associated with information for specifying a particular area in the storage apparatus.
Moreover, Japanese Patent Application Laid-open Publication No. 10-289189 discloses that, when an I/O sub-system is in a high load status due to an accumulation of I/O requests to a particular apparatus, a reduction in the throughput of the whole computer system is prevented by automatically restricting the issue of I/O requests to the particular apparatus while preferentially issuing I/O requests to another apparatus.
Meanwhile, Japanese Patent Application Laid-open Publication No. 6-35831 discloses a technique for reducing a waiting time of input/out processing for data with high priority. Specifically, when multiple data input/output instructions are issued at the same time, a backlog of data input/output processing is caused. To deal with the backlog, the order of processing is determined by first-preferentially selecting a data input/output instruction with high data input/output priority, and then by second-preferentially selecting a data input/output instruction targeting a location that is the nearest to a location where the last data input/output processing has been performed.
By the way, in an information processing system having an information apparatus and a storage apparatus coupled to each other through a plurality of paths may use, for example, the following algorithms in order to balance the loads among the paths: an algorithm that sets weights in respective plurality of paths to issue an I/O to each of the paths according to the weights thus set; and an algorithm that preferentially issues I/Os to a path that has a lower load. However, adopting such algorithms may increase the load on a particular one of the paths because multiple I/Os may be issued to the particular path during a short period of time and in a concentrated manner, and thereby may impair the effect of the load balancing.